Summary: A spent lime residue from an atmospheric fluidized bed combustion process was used to modify two highway soil subgrade sections on a route in Kentucky. The AFBC residue contains high percentages of CaO, Ca(OH)2, and MgO and produces soil-lime pozzolanic reactions when mixed with clayey soils to form cementing-type materials. About two months after stabilization, non-uniform heave occurred in the asphaltic base course surface. Final surfacing was delayed and field and laboratory studies were initiated. Long-term swell test, lasting up to 186 days, were performed on compacted specimens containing different percentages of the spent lime residue and subgrade soils. Optical survey points established on the pavement surfaces were monitored over a period of about 5.5 years.